1. Field of the Invention
The present invention relates to a spiral-spring driving unit for use with a toy vehicle, and more particularly to a spiral-spring type driving unit employed in a toy vehicle which causes the spiral-spring type driving unit to store a sufficient energy therein when being moved backward by a relatively short disease, the thus stored energy being released to rotatably drive a driving axle of the toy vehicle so as to make it possible that the toy vehicle travels a relatively long distance.
2. Description of the Prior Art
In this spiral-spring type of driving unit, in order to ensure a relatively long travel distance for the toy vehicle in case that the toy vehicle is moved backward by a relatively short distance for storing energy therein, an input gear train of the driving unit differs from an output gear train of the same unit in gear ratio. Consequently, in any of conventional driving units, there are provided a pair of idle gears so as to provide an independent input and an independent output gear trains, which makes the driving unit complex in construction. However, it is preferable for the driving unit to be as small a size and as simple a construction as possible for use wth the toy vehicle, provided that the driving unit is sufficiently high in efficiency. Under such circumstances, there is a strong demand for developing such small-sized and simple construction driving unit with a high efficiency for use of the toy vehicle.
Hitherto, although many types of such driving units have been proposed, any of them is too complex in construction.
For example, U.S. Pat. No. 4,463,831 discloses one of such driving units, which is provided with a pair of idle gears fixedly mounted on rotary shafts which are supported by oblong bearing holes provided in three supporting plates, respectively. As described above, since the driving unit disclosed in the above U.S. Pat. employs such pair of idle gears, it is necessary for the driving unit to employ at least three supporting plates for defining a pair of gear housings, through which supporting plates are rotatably and swingably supported a pair of rotary shafts of the idle gears. As a result, it is necessary for the driving unit to employ at least five gears and five rotary shafts thereof in total, which makes the driving unit complex in construction.
In addition, in the driving unit disclosed in the above U.S. Patent, it is hard to wind up the spring of the driving unit in a condition in which the driving unit is turned upside down.